could use some help

[bob163]

hello all
i just got a 2005 3500 great boat but having a real issue port side engine seems to surge wont hold idle and very rough start when i push it up over 2000 rpm she will hold but difficult to get there cause i have to race it in neutral so far i did
all filters and good fuel
plugs cap rotor
iac
tps
fuel pump
i will take any and all ideas thanks
bob m
oh 5.0 merc mpi

[Phillbo]

Water in fuel....

[bob163]

i thought that but fuel is fresh new filters and starboard runs like a top off same tank

[mmwjr]

Did you use a OEM IAC, if not I would do as others have reported issues with this. Did you replace the IAC filter (muffler) these get clogged and can cause your issue?